All of the non-transparent pixels in a sprite can cause a collision. If you use the sprite on top of the text screen or hi-res bitmap then any pixels that touch will cause a collision.
But if you use a sprite on top of a multi-color bitmap, then only bitmap colors 2 and 3 will cause a collision. Bitmap colors 0 and 1 are considered 'background' and will not cause a collision.
The easiest way for me is to create sprites using SPRDEF then save them to disk with a command
BSAVE"SPRITES",B0,P3584 TO P4096
To load them back just use
You can add ",P3584" to specify the start address but you don't need to if you saved it like the example above (which writes the start address into the file header).
There are several editors available for the PC, but I haven't used any of them (old school baby). The most recent that comes to mind is CBM .prg Studio
. This lets you create sprites, charsets, and even write programs and test them on your PC. I don't know how difficult it would be to take a sprite from that and load into your own program, but it shouldn't be too difficult.